FIG. 1 shows a schematic circuit diagram of the conventional radio frequency receiver.
As shown in FIG. 1, the conventional radio frequency receiver comprises a low-noise amplifier 110, first and second mixers 120, 130, a local oscillator 140 and first and second base-band circuits 150, 160.
Low-noise amplifier 110 amplifies radio frequency signal received by an antenna to apply the signal to first and second mixers 120, 130. First and second mixers 120, 130 mix the amplified radio frequency signal with in-phase local oscillating signal LOI and quadrature-phase local oscillating signal LOQ to output intermediate frequency or base band signal, respectively. First and second base-band circuits 150, 160 amplify/filter the signal outputted from first and second mixers 120, 130, respectively to output in-phase signal I and quadrature-phase signal Q.
In radio communication system, radio frequency receiver transmits data by carrying it in in-phase channel and quadrature-phase channel. Thus, in order to restore signal completely, in-phase local oscillating signal LOI and quadrature-phase local oscillating signal LOQ are necessary. If the difference between the phases of LOI and LOQ does not equal 90 degree, bit error rate increases in the restored signal. In particular, tile mismatch between in-phase signal I and quadrature-signal Q causes significant problem in the system of direct-conversion receiver and image-removing receiver.
However, the characteristic of delay cells of the local oscillator does not ideally match due to thickness of insulator, device size, space difference, various crystal structure of semiconductor material, mismatch of layout and the like. Such a mismatch of delay cells causes mismatch between in-phase local oscillating signal LOI and quadrature-phase signal LOQ outputted from the local oscillator. This is an important cause of generating mismatch between I/Q signals of the receiver. Further, mismatch between devices in way of I and Q path of the receiver is one of causes generating I/Q mismatch of radio frequency receiver.
As clearly understood from a person skilled in the art, size mismatch between in-phase signal I and quadrature-phase signal Q is not significant cause. However, phase mismatch may cause significant problem due to path difference between two signals and device characteristic as frequency increase.
In conventional art, the phase mismatch is corrected with compensation of in-phase signal I and quadrature-phase signal Q of base band that pass a mixer or with compensation of the paths of radio frequency signals I and Q. However, these corrections require additional correction circuit in signal path. The addition of correction circuit to a path where signal passes may degrade gain, noise, linearity and the like. Further, it is difficult to apply the technique in already-manufactured circuit,